Conventionally, modular computers are composed of electronic boards assembled and held in a chassis within slide rails perpendicular to the backplane. The electronic boards are parallel to one another. An electronic board comprises components. In operation, the components of the electronic board can dissipate a large quantity of heat. This heat must be evacuated in order to maintain a suitable operating temperature.
Two main categories of cooling exist: cooling by thermal convection and cooling by thermal conduction.
Thermal convection consists in bringing a warm body into contact with a fluid. A part of the thermal energy of the warm body is transferred to the fluid. In the field of electronics, cooling by thermal convection generally takes place with a gaseous fluid, for example air. For a better convection, it is possible to force the circulation of the fluid. For example, fans may be used in order to increase the circulation of air over the warm components on the electronic board. The heat exchange between the warm components and the air is thus improved.
Thermal conduction is a mode of heat transfer resulting from a difference in temperature between two regions of the same medium or between two different media in contact. Cooling by thermal conduction is sometimes preferred to cooling by convection in harsh environments, notably for reasons of reliability (no mobile element such as a fan) and of sealing against contaminants (dust particles, etc.). Thermal conduction cooling is one of the modes of cooling chosen for embedded modular computers.
In an electronic board, cooling by thermal conduction takes place by virtue of a thermal drain. The thermal drain is formed from a plate which can for example be made of copper, aluminium or composite materials. The thermal drain may be disposed on top of the electronic board parallel to the plane of the printed circuit. It matches the shape of the components on the board. Two locking means, known as ‘wedgelocks’ or ‘cardlocks’ in the literature, are positioned along the two edges of the board perpendicular to the backplane in order to hold the electronic board and its thermal drain tight in a chassis. The locking means is an expandable locking means which presses the thermal drain against one slide rail of the chassis. The chassis represents the cold medium. The thermal drain allows the evacuation of the heat by conduction between the hot components on the board and the chassis. The pressure of the thermal drain against the cold medium ensures a good contact and hence an efficient heat exchange.
Currently, for a version of board using conduction cooling mode, since the locking of the electronic board with its thermal drain is achieved by means of a standard locking means, the edges of the printed circuit need to be cut out. This cutting out has many drawbacks. Indeed, depending on the mode of cooling, convection or conduction, two formats of printed circuit need to be provided. This therefore requires the fabrication and the storage of two different formats of printed circuits. In addition, in order to go from a printed circuit using cooling by convection to a printed circuit using cooling by conduction, a cutting out of the printed circuit needs to be implemented. The cutting out of a printed circuit is a sensitive process. The tolerances of the cut-out with respect to the copper tracks need to be adhered to, and there is a risk of scattering of cut-out residues over the whole electronic board. Finally, with a view to a possible cutting out of the printed circuit in the case of cooling by conduction, it may not be envisaged for this part of the board to be used for the positioning of tracks or of components.